Twig.php: Twig supports the in operator

A few fixes for Twig.php's test/Twig/Tests/Fixtures/tests/in.test

Twig.js generates too many newlines compared to Twig.php. In PHP newlines directly after PHP-tags are ignored, Twig.php has the same behavior after logic-tokens.

And 
```
{% if '' not in bar %}
```

String.prototype.indexOf( ) return index 0 if you look for an empty string and in Twig.php's test case this should be false.